Sharpening without burning

[tesseract]

I am new to the art of metalworking and do not have that much knowledge accordingly.

I have a bunch of 1/8" hardened steel dowel pins 3/4" long I want to cut one end at a 45 degree angle and then sharpen it and I want to have it holds it sharpness as long as possible it will be cutting through 2 liter plastic bottles. I know I can easily grind it down but I want to keep the metals hardness.

In my passed naivety I would have just cut them and continued but I want to do this right so I am asking. I don't have access to laser cutters or anything like that just normal stuff you would find in a small garage i do have a grinder but not I do not want to burn the metal.

Can someone please help
What is the trick to bring an edge to a piece of metal that will hold with out burning it or having to re-harden it

Thanks

 

[zkling]

Depends on how patient you are.

If you do it by hand (files, stone and paper) you will have no problem keeping it cool, but may have a hard time keeping YOUR cool

Under power you could use a slow running grinder, a wet grinder or a standard bench grinder, light pressure and frequent dunking of the pin into a trough of water.

1/8" isn't much material, so paper wouldn't be to bad. And like wise, frequent dunking on the grinder wouldn't be bad either since you don't have much material to remove. Just remember that the "sharp" edge where it is the thinnest, will get heated the fastest. Basically you will just be alternating between touching the grinding wheel and dunking into water.

 

[tesseract]

1/8" isn't much material, so paper wouldn't be to bad.

You mentioned this and I am confused what do you mean paper

According o what you have stated I will be trying my bench grinder on the straight pin and plan to grind down to the 45 degree angle to get my sharpened edge.and will alternate between grinding and dunking in water

I plan to make a jig so I can get them all to be the same.

Would it be any benefit to have the wheel itself wet

I do have some sharpening stones as well would you think that would benefit me to go over them all with a sharpening stone as well or will the grinder suffice.

I have a box of 100 coming in but need about 72 for my project so I do have some extras to play with

 

[zkling]

By paper, I mean sand paper. Something high quality, wet dry.

Ouch, 72? What are you building? It may benefit you to just purchase standard bar stock, cut, sharpen and then heat treat after. Hand sharpening 72 pieces that are 3/4" long is going to be real tedious without a jig.

Yes you can run coolant on a grinding wheel, but it will be very messy and not good for a standard bench grinder. Industrial bench grinders come with small trays for water to prevent overheating when sharping lathe tooling, drill, etc.

One thing to keep in mind. Most dowel pins are case hardened, so when you grind off the end, only an oval-ish portion of your cutting edge is going to be hardened. Are you trying to make a needle type of thing? If you are only cutting though plastic bottles, I wonder if you are over thinking this.

 

[larry_g]

zkling gave you good advise. Patience will get the job done. That said I have to ask why you chose a dowel to make a cutter instead of a high speed steel, HSS, to make your cutter? I think your going to find the plastic bottle quite abrasive and prone to dulling your tool perty fast. So selecting the proper material is to your advantage at the start of the project. Look into using drill rod instead.

lg
no neat sig line

 

[tesseract]

zkling gave you good advise. Patience will get the job done. That said I have to ask why you chose a dowel to make a cutter instead of a high speed steel, HSS, to make your cutter? I think your going to find the plastic bottle quite abrasive and prone to dulling your tool perty fast. So selecting the proper material is to your advantage at the start of the project. Look into using drill rod instead.

lg
no neat sig line

I do appreciate the advise and I am trying to take it all in I did look at drill rod S7 was the stuff I was going with but after I did all the cutting into 3/4" lengths with a 45 on one end the cost to heat treat --harden-- them was quoted twice between $100 and $200 bucks and I am trying to keep this low cost

box of 100 hardened steel pins was $6.00


Here is a basic overview of it
The oval that would still be hardened is perfect as these will become teeth in a spindle that will pass through a metal comb plate made for these pin sizes the plastic will go between. I positioned the angle of the combplate downward to such an angle that the impact point with the plastic will be the tip and then as the side move through the comb it will simply shear of little pieces so the cutting edge will actually be the oval sides

The rows in the spindle are offset in two ways

if the cutting pattern in a straight line were as follows
1 2 3 4 5 6 7 8 9 ...24

Each alternating row cuts the even spaces or the odd spaces and each row of pins is actually offset from each other by about 10mm so in the case of a single row as the spindle rotates row 1 would cut space 1 then the spindle moves 10 mm in rotation and then pin 3 , then pin 5, then pin 6, etc. about halfway through the first row of pins doing a cut, the second row starts so then pin 2, pin 4, pin 6 etc. I did this to avoid having the plastic jam up.

I attached a top view of the cylinder showing how the pins would be oriented the plastic would be meeting the cutting pins at about the 8 o'clock position. At 9 the pin would simply slap flatly directly against the plastic at 8 the tip goes in first.

 

[metal1313]

so your basically making a circular blade?

you have any drawings of what your making. i have a bottle shreader in my mind, but im not sure.

 

[tesseract]

not a complete drawing yet mainly the cylinder assembly

 

[theoldwizard1]

Under power you could use a slow running grinder, a wet grinder or a standard bench grinder, light pressure and frequent dunking of the pin into a trough of water.

Yep !

 

[DoghouseForge]

If you don't already have one go get a cheap 1x30" belt sander. then on. EBay look up 1x30" sanding belts. Order the klingspor 120 grit and 320 grit.

As stated above get a bowl of water and cool the tip after each pass. 120 to eat it and 320 to finish it. Personaly I wouldn't use the stones on the grinder. Instead get a buffing wheeland some finishing rouge. Put your final edge on with the cloth Wheel.

All of this stuff is available cheap at the same china made tool store. Not my favorite choice but good when your gonna just do the project one time.

If your grinding and you get a blue color you got the steel up to about 600 degree. Yellow is about 400deg. If you reach that blue tint on accidentlet that piec cool a few minutes and then quench it. If ypu cool it from to hot to fast it will harden to much and be hard to finish sharping.

I understand the cost issues but by not using a high carbon tool steel even your best effort is going to result in a shorter life span for your saw.

Hope this helps

JP

 

[Kevin54]

I take it you're making some sort of cutter or shredder. One thing is with dowel pins, they're "case hardened". That means the center is not as hard as you may need. What you want to use would be more along the lines of a drill blank. Drill blanks are hardened all of the way through.

Now if you are wanting to make something that is precision, you'll need a jig to set the pins in and they should be ground on a surface grinder. In doing so, you can grind a little and let them cool, or if they are ground under coolant, then there would be no problem at all.

What I see from your drawings is that you are basically making something to shread the bottles, correct? The reason I ask is that if you have the pins cut on a 45 degree angle on the end, how are you going to index the pins in the hub you're putting them in? And once indexed to the correct position, how do you plan on the pins staying in the holes in the hub? I understand what you envision, but there is more involved than just sticking a pin in a hole.

If the pin is to be press fit into the holes, then it will have to be sharpened after the fact of press fitting them in. If they are sharpened before hand, and you want to press them in, then you are going to dull the edge. Also, with the cutters being round, you won't have the cutting surface that you envision, as the only area doing any cutting will be right at the tip, anything past that area will just be pushing the material off to the side as the round pins will widen out.

A simple jig can be made to grind the pins at a 45 as long as your grinder has a table of some sort that you could have some sort of reference area that would keep the fixture at the same place consistently.

If you would, explain a little more as to what you are trying to accomplish and some members may be able to come up with a simpler solution with what you are trying to do.

 

[blackz26]

Why not just go get the size drill bit you want? Its just plastic.... sounds like a lot of wasted time and effort..

 

[ilovevocs]

Whats stopping you from using o1 drill rod and hardening at home with a propane torch and a tin of oil?

Im not an expert machinist but made my own center punches following guidelines from the home shop machinist.

Heat the point to cherry red, swirl in oil to cool, then anneal by heating to a blue color and allow it to air cool. The color used during annealing affects the hardness.

Also could consider using mild steel and case hardening using Kasenit.

I did a quick search and found this how-to.

http://occhiolungo.wordpress.com/2010/10/10/how-to-heat-treating-at-home/

 

[zoowho2]

I am new to the art of metalworking and do not have that much knowledge accordingly.

I have a bunch of 1/8" hardened steel dowel pins 3/4" long I want to cut one end at a 45 degree angle and then sharpen it and I want to have it holds it sharpness as long as possible it will be cutting through 2 liter plastic bottles. I know I can easily grind it down but I want to keep the metals hardness.

In my passed naivety I would have just cut them and continued but I want to do this right so I am asking. I don't have access to laser cutters or anything like that just normal stuff you would find in a small garage i do have a grinder but not I do not want to burn the metal.

Can someone please help
What is the trick to bring an edge to a piece of metal that will hold with out burning it or having to re-harden it

Thanks

Lots of dunking in wa wa and patience. Get and use a diamond wheel, a bit expensive but a very hard fine grinding wheel used mainly for tool bit sharpening, carbide and other extremely hard metals and use with patience and constant dipping. Fine diamond bits are embedded and remove material easily and smoothly..don't force, it will cut just fine with very little pressure. You can also use a coolant sprayas you grind..messy but saves the tool and wheel..or a drip dribble tube on grind point..messy but so is *** and well worth it.

 

[Kevin54]

Lots of dunking in wa wa and patience. Get and use a diamond wheel, a bit expensive but a very hard fine grinding wheel used mainly for tool bit sharpening, carbide and other extremely hard metals and use with patience and constant dipping. Fine diamond bits are embedded and remove material easily and smoothly..don't force, it will cut just fine with very little pressure. You can also use a coolant sprayas you grind..messy but saves the tool and wheel..or a drip dribble tube on grind point..messy but so is *** and well worth it.

One thing to beware of....if you get a smooth diamond wheel that is used mainly for grinding carbide, you don't want to use dowel pins on it. If you do it will load up the wheel. Dowels are only case hardened anyways. Not food for making something and wanting to to stay sharp.

I don't think the OP is around anyways. After he posted and people answered his questions, he hasn't been back on.

 

[Clik]